Room Suggestion

If you're asking which room to use I'd use the basement or the second room. If you don't mind building a room in the basement that would be my pick. That's exactly what I did here. The best thing about it is I used soundboard, resilient channel then drywall then acoustic tiles on the ceiling. This helps isolate you from the rest of the house. I can play my stereo quite loudly without bothering the two women upstairs. Get some bass traps and treat at least all the first reflection points and you'll have a very nice listening room.

Having a sloped ceiling like room number two is good but at 55" is awfully low. The other two rooms are too small unless you listen to low levels and treat it well. Room acoustics/treatment is well worth the money and is a better investment than upgrading electronics.

Extrastrong: Soundboard comes in 4x8 sheets and supposedly helps damp sound more than an extra layer of sheetrock. From what I gather it appears just an extra layer of sheetrock would be fine although is about the same price if I remember correctly. You need to use sheetrock for ceilings, can't remember what it's called, so it can't sag.

Resilient channel can also be purchased at a construction supplier, not Home Depot or Lowes though at least here.
You'll have to see it to understand but you screw the sheetrock to it and the sheetrock actually hangs from it allowing the sheetrock to vibrate without vibrating the rafters much. It's cheap and well worth it.

I have two systems down here in the basement. With my little system in my computer room the sound goes straight through the floor. In my big system I can crank it and you can hear some bass but that's about it. With the small system I have to keep it turned down! My main speakers outweigh my little ones by 240lbs a piece.

You can email me if you need any more help. You'll be very glad you did this.